Precursor for preparation of lithium composite transition metal oxide, method for preparing the same and lithium composite transition metal oxide obtained from the same

ABSTRACT

Disclosed are a precursor for preparation of a lithium composite transition metal oxide, a method for preparing the same and a lithium composite transition metal oxide obtained from the same. More particularly, the transition metal precursor which has a composition represented by Formula 1 below and is prepared in an aqueous transition metal solution, mixed with a transition metal-containing salt, including an alkaline material, the method for preparing the same and the lithium composite transition metal oxide obtained from the same are disclosed.
 
Mn a M b (OH 1-x ) 2-y A y   (1)
         wherein M is at least one selected form the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and Period II transition metals; A is at least one selected form the group consisting of anions of PO 4 , BO 3 , CO 3 , F and NO 3 , and 0.5≤a≤1.0; 0≤b≤0.5; a+b=1; 0&lt;x&lt;1.0; and 0≤y≤0.02.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national phase entry under 35 U.S.C. § 371 ofInternational Application No. PCT/KR2014/007613, filed Aug. 18, 2014,which claims priority to Korean Patent Application No. 10-2013-0098746,filed Aug. 20, 2013, the disclosures of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a precursor for preparation of alithium composite transition metal oxide, a method for preparing thesame and a lithium composite transition metal oxide obtained from thesame. More particularly, the present invention relates to a transitionmetal precursor which has a specific composition and is prepared in anaqueous transition metal solution, mixed with a transitionmetal-containing salt, including an alkaline material, a method forpreparing the same and a lithium composite transition metal oxideobtained from the same.

BACKGROUND ART

As mobile device technology continues to develop and demand thereforcontinues to increase, demand for secondary batteries as energy sourcesis rapidly increasing. Among these secondary batteries, much researchhas focused on lithium secondary batteries having high energy densityand discharge voltage. Such batteries are commercially available andwidely used.

Generally, as cathode active materials for lithium secondary batteries,lithium-containing cobalt oxides such as LiCoO₂ are mainly used. Inaddition thereto, use of lithium-containing manganese oxides such asLiMnO₂ having a layered crystal structure, LiMn₂O₄ having a spinelcrystal structure, and the like and lithium-containing nickel oxidessuch as LiNiO₂ is also under consideration.

Among cathode active materials, LiCoO₂ is widely used due to excellentoverall physical properties such as excellent cycle properties, and thelike. However, LiCoO₂ is low in safety and expensive due to resourcelimitations of cobalt as a raw material. Lithium nickel based oxidessuch as LiNiO₂ are cheaper than LiCoO₂ and exhibit high dischargecapacity when charged to a voltage of 4.25 V. However, the lithiumnickel based oxides have problems such as high production costs,swelling due to gas generation in batteries, low chemical stability,high pH and the like.

In addition, lithium manganese oxides, such as LiMnO₂, LiMn₂O₄, and thelike, are advantageous in that they contain Mn, which is an abundant andenvironmentally friendly raw material, and thus are drawing muchattention as a cathode active material that can replace LiCoO₂. Inparticular, among the lithium manganese oxides, LiMn₂O₄ has advantagessuch as a relatively cheap price, high output and the like. On the otherhand, LiMn₂O₄ has lower energy density, when compared with LiCoO₂ andthree component-based active materials.

To overcome these drawbacks, a variety of materials have been developed.Especially, layered structure transition metal oxides such asLiNi_(1/3)Mn_(1/3)Co_(1/3)O₂, LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ and the likeincluding two or more materials of Ni, Mn and Co have been highlighted.

However, these materials do not satisfy requirements of medium and largebatteries such as those used in electric vehicles, systems for storingpower and the like.

Accordingly, study into Mn-enriched (1−x)LiMO₂-xLi₂MO₃ based materialsstable under high voltage is being conducted. However, the Mn-enriched(1−x)LiMO₂-xLi₂MO₃ based materials include a large amount of Mn andthereby are easily oxidized by dissolved oxygen inside an aqueoustransition metal solution during synthesis of a transition metalprecursor through a co-precipitation method, and, accordingly, synthesisis not easy.

To compensate for this problem, methods such as surface treatment,formation of a core-shell structure and substitution with heteroelements and the like have been tried. However, the methods also are notsuitable for easy synthesis. In addition, there are still problems suchas additional costs during processes, deterioration of precursor tapdensity and the like.

As described above, a precursor for preparation of a lithium compositetransition metal oxide having satisfactory performance and a lithiumcomposite transition metal oxide obtained from the same has yet to bedeveloped.

DISCLOSURE Technical Problem

The present invention aims to address the aforementioned problems of therelated art and to achieve technical goals that have long been sought.

As a result of a variety of extensive and intensive studies andexperiments, the inventors of the present invention developed atransition metal precursor having a specific composition resulting inimprovements in crystallizability, spheroidization degree of apulverulent body and tap density, and confirmed that, when a lithiumcomposite transition metal oxide prepared using the transition metalprecursor was used as a cathode active material, an electrodepreparation process is easy and electrochemical characteristics of asecondary battery based on the lithium composite transition metal oxideare improved, thus completing the present invention.

Technical Solution

In accordance with one aspect of the present invention, provided is atransition metal precursor, having a composition represented by Formula1 below, prepared in an aqueous transition metal solution mixed with atransition metal-containing salt and including an alkaline material:Mn_(a)M_(b)(OH_(1-x))_(2-y)A_(y)  (1)

wherein M is at least one selected form the group consisting of Ni, Ti,Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and Period □ transition metals;

A is at least one selected form the group consisting of anions of PO₄,BO₃, CO₃, F and NO₃; and0.5≤a≤1.0; 0≤b≤0.5;a+b=1; 0<x<1.0; and 0<y≤0.02.

In Formula 1, x may be particularly 0.2 or more and less than 0.5, moreparticularly, 0.3 or more and less than 0.5.

In one specific embodiment, oxidation number of Mn may be +2 to +3.5.

In one specific embodiment, the transition metal precursor according thepresent invention may be prepared using a co-precipitation method.Through the co-precipitation method, at least two transition metalelements are co-precipitated by precipitation reaction in an aqueoussolution. In a specific embodiment, a transition metal precursorincluding at least two transition metals may be prepared by mixingtransition metal-containing salts in a desired molar ratio inconsideration of the amounts of the transition metals to prepare anaqueous solution and then by performing co-precipitation whilemaintaining the resulting solution at alkaline PH by adding a strongbase such as sodium hydroxide or the like and, if necessary, an additivesuch as ammonia or the like.

Here, desired average particle diameter, particle diameter distributionand particle density may be adjusted by appropriately adjustingtemperature, pH, reaction time, slurry concentration, ion concentration,and the like. In this regard, pH may be in the range of 9 to 13, forexample, in the range of 9 to 12, and, in some cases, reaction may beperformed in multiple steps.

However, when the fraction of Mn in the composition is 0.4 or more, Mnis readily oxidized by dissolved oxygen inside an aqueous transitionmetal solution during a preparation process of the precursor and, assuch, uniform precipitation of transition metal elements is difficult.

Accordingly, in one specific embodiment, the transition metal precursormay further include a reducing agent to prevent oxidation of Mn andthereby the transition metal precursor has a uniform diameter.

The reducing agent may be included in 0.1 to 30 mol %, particularly, 1.0to 10 mol %, based on the molar amount of the aqueous transition metalsolution. When the amount of the reducing agent is less than 0.1 mol %,it is not easy to prevent oxidation of Mn due to too small amount of thereducing agent. On the other hand, when the amount of the reducing agentexceeds 30 mol %, the transition metal hydroxide has stronganti-precipitation tendency and, as such, characteristics of apulverulent body may be deteriorated.

In one specific embodiment, the reducing agent may be at least oneselected form the group consisting of hydrazine, oxalic acid, ascorbicacid, and particularly a sugar-based material.

The sugar-based material may be at least one selected form the groupconsisting of, for example, fructose, sucrose, glucose, galactose,lactose, maltose, starch, and dextrin.

When the sugar-based material is used as a reducing agent, thesugar-based material exists on a surface of the transitionmetal-containing salt and thus prevents cohesion of particles.Accordingly, a transition metal precursor having high porosity and alarge specific surface area may be prepared. In addition, thesugar-based material may exist in inner pores or on a particle surfaceof the transition metal precursor. Furthermore, the reducing agentexisting inside the transition metal precursor is carbonized and somereducing agent exists, and, as such, the transition metal precursor hascarbon treatment effects. Accordingly, after sintering, electrochemicalcharacteristics may be improved.

Although the transition metal precursor has the advantages describedabove by adding the reducing agent, the tap density of the pulverulentbody may be reduced and thereby an electrode process may becomedifficult, due to relatively high porosity.

The inventors of the present invention realized the above problem and,as a result of intensive and extensive studies, discovered that thetransition metal hydroxide may be more easily precipitated and cohesiveforce of particles may be improved, and, as such, the crystallizability,spheroidization degree and tap density of the transition metal precursormay be improved, in spite of addition of the reducing agent, bysubstituting anion sites with anions of PO₄, BO₃, CO₃, F, NO₃ and thelike during a preparation process of a transition metal precursorcontaining a high manganese content. The inventors of the presentinvention also discovered that, when a lithium composite transitionmetal oxide is prepared using the transition metal precursor, anelectrode process is easy and a secondary battery including thetransition metal precursor as a cathode active material has superiorinitial discharge capacity and efficiency, and improved outputcharacteristics.

However, when the amount of substituted anions exceeds 0.02, charge anddischarge capacity, and efficiency are greatly reduced. Therefore, theamount of substituted anions exceeding 0.02 is not preferable.

In one specific embodiment, as the transition metal-containing salt, atransition metal-containing salt having anions easily decomposed andvolatilized during sintering is preferable. The transitionmetal-containing salt may be sulfates, nitrates or carbonates. Asspecific examples, the transition metal-containing salt may be nickelsulfate, manganese sulfate, nickel nitrate, manganese nitrate, nickelcarbonate, manganese carbonate or the like, but the present disclosureis not limited thereto.

In addition, the alkaline material may be sodium hydroxide, potassiumhydroxide, lithium hydroxide or the like, preferably sodium hydroxide.However, the present disclosure is not limited thereto.

The present invention also provides a method of preparing the transitionmetal precursor.

In particular, the transition metal precursor according to the presentinvention may be prepared according to a method including:

(i) preparing an aqueous transition metal solution including atransition metal-containing salt for preparing a precursor;

(ii) mixing anions with the aqueous transition metal solution tosubstitute anion sites of the precursor; and

(iii) co-precipitating by adding a strong base after the mixing.

The anions may be added by mixing with other materials such as atransition metal-containing salt or the like during the precursorsynthesis process so long as other side reaction does not occur, or maybe separately added. However, in consideration of process costreduction, the anions are preferably added by mixing with othermaterials.

In one specific embodiment, in step (ii), a reducing agent, besidesanions, may be further added and mixed.

Here, the reducing agent may be added at the same time with a materialsuch as the transition metal-containing salt or the like or may beseparately added. When the reducing agent is separately added, additionamount per hour, the concentration of the reducing agent or the like maybe an important variable in precursor formation.

In one specific embodiment, the concentration of the reducing agent maybe 2.0 mol % to 7.0 mol %. When the concentration of the reducing agentis less than 2.0 mol %, desired effects are insignificant. On the otherhand, when the concentration of the reducing agent exceeds 7.0 mol %,precipitation of the precursor is excessively suppressed.

In addition, in the co-precipitating of step (iii), an additive and/oralkali carbonate which may form a complex with a transition metal may befurther added. The additive may be, for example, an ammonium ion source,ethylenediamine class compounds, citric acid class compounds or thelike. The ammonium ion source may be, for example, aqueous ammonia,aqueous ammonium sulfate solution, aqueous ammonium nitrate solution orthe like. The alkali carbonate may be selected from the group consistingof ammonium carbonate, sodium carbonate, potassium carbonate and lithiumcarbonate. In this case, as desired, two or more carbonates from thegroup may be selected and mixed.

Addition amounts of the additive and alkali carbonate may be properlydetermined considering the amount of the transition metal-containingsalt, pH and the like.

The present invention also provides a lithium composite transition metaloxide prepared using the transition metal precursor. In particular, alithium composite transition metal oxide as a cathode active materialfor lithium secondary batteries may be prepared by mixing the transitionmetal precursor with the lithium precursor and reacting the resultingmixture through sintering under an oxidizing atmosphere.

The lithium precursor, which is not specifically limited, may be, forexample, lithium hydroxide, lithium carbonate, lithium oxide or thelike. The lithium precursor is preferably lithium carbonate (Li₂CO₃)and/or lithium hydroxide (LiOH).

In one specific embodiment, the lithium composite transition metal oxidemay be represented by Formula 2 below.(1−x)LiM′O_(2-y)A_(y)-xLi₂MnO_(3-y′)A_(y′)  (2)

wherein M′ is Mn_(a)M_(b);

M is at least one selected form the group consisting of Ni, Ti, Co, Al,Cu, Fe, Mg, B, Cr, Zr, Zn and Period II transition metals;

A is at least one selected form the group consisting of anions of PO₄,BO₃, CO₃, F and NO₃; and0<x<1; 0<y≤0.02; 0<y′≤0.02; 0.5≤a≤1.0; 0≤b≤0.5; and a+b=1.

In the lithium composite transition metal oxide, anion sites of whichare substituted, ionic conductivity is improved by anions and structuralchange due to gas occurring at a battery activation step is reduced.

In one specific embodiment, the lithium composite transition metal oxiderepresented by Formula 2 may be a solid solution and composite form. Inthis case, as desired, the lithium composite transition metal oxide maybe a mixture of the solid solution and composite form.

Inventors of the present application confirmed that the lithiumcomposite transition metal oxide may be effectively synthesized usingthe transition metal precursor according to the present invention and,when the transition metal precursor was used as a cathode activematerial in a lithium secondary battery, the lithium secondary batterywas stable under high voltage, and exhibited superior initial dischargecapacity and efficiency, and improved output characteristics andlifespan characteristics.

The lithium composite transition metal oxide may be preferably used asan electrode active material for lithium secondary batteries. Thelithium composite transition metal oxide may be separately used or maybe used by mixing with other publicly known electrode active materialsfor lithium secondary batteries.

Reaction conditions of the transition metal precursor and thelithium-containing material to prepare the lithium composite transitionmetal oxide are publicly known in the art. Therefore, detaileddescriptions of the reaction conditions will be omitted in thespecification.

The present invention also provides a cathode including the lithiumcomposite transition metal oxide as a cathode active material and alithium secondary battery including the same.

For example, the cathode is prepared by drying after coating a mixtureof the cathode active material according to the present invention, aconductive material and a binder on a cathode current collector. In thiscase, as desired, the mixture may further include a filler.

The cathode current collector is generally fabricated to a thickness of3 to 500 μm. The cathode current collector is not particularly limitedso long as it does not cause chemical changes in the fabricated lithiumsecondary battery and has high conductivity. For example, the cathodecurrent collector may be made of stainless steel, aluminum, nickel,titanium, sintered carbon, aluminum or stainless steel surface-treatedwith carbon, nickel, titanium, or silver, or the like. The cathodecurrent collector may have fine irregularities at a surface thereof toincrease adhesion between the cathode active material and the cathodecurrent collector. In addition, the cathode current collector may beused in any of various forms including films, sheets, foils, nets,porous structures, foams, and non-woven fabrics.

The conductive material is typically added in an amount of 1 to 20 wt %based on the total weight of the mixture including the cathode activematerial. There is no particular limit as to the conductive material, solong as it does not cause chemical changes in the fabricated battery andhas conductivity. Examples of conductive materials include graphite suchas natural or artificial graphite; carbon black such as carbon black,acetylene black, Ketjen black, channel black, furnace black, lamp black,and thermal black; conductive fibers such as carbon fibers and metallicfibers; metallic powders such as carbon fluoride powder, aluminumpowder, and nickel powder; conductive whiskers such as zinc oxidewhiskers and potassium titanate whiskers; conductive metal oxides suchas titanium oxide; and polyphenylene derivatives.

The binder is a component assisting in binding between an activematerial and the conductive material and in binding of the activematerial to a current collector. The binder is typically added in anamount of 1 to 20 wt % based on the total weight of the mixtureincluding the cathode active material. Examples of the binder include,but are not limited to, polyvinylidene fluoride, polyvinyl alcohols,carboxymethylcellulose (CMC), starch, hydroxypropylcellulose,regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene,polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM),sulfonated EPDM, styrene butadiene rubber, fluorine rubber, and variouscopolymers.

The filler is optionally used as a component to inhibit cathodeexpansion. The filler is not particularly limited so long as it is afibrous material that does not cause chemical changes in the fabricatedbattery. Examples of the filler include olefin-based polymers such aspolyethylene and polypropylene; and fibrous materials such as glassfiber and carbon fiber.

Generally, the lithium secondary battery includes the cathode, an anode,a separator and a lithium salt-containing non-aqueous electrolyte. Theother components of the lithium secondary battery according to thepresent invention will be described below.

The anode may be prepared by coating and drying an anode material on ananode current collector. As desired, the anode material may furtherinclude the above-described components.

Examples of the anode active material include carbon such as hard carbonand graphite-based carbon; metal composite oxides such as Li_(x)Fe₂O₃where 0≤x≤1, Li_(x)WO₂ where 0≤x≤1, Sn_(x)Me_(1-x)Me′_(y)O_(z) where Me:Mn, Fe, Pb, or Ge; Me′: Al, B, P, Si, Group I, II and III elements, orhalogens; 0<x≤1; 1≤y≤3; and 1≤z≤8; lithium metals; lithium alloys;silicon-based alloys; tin-based alloys; metal oxides such as SnO, SnO₂,PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄,and Bi₂O₅; conductive polymers such as polyacetylene; and Li—Co—Ni-basedmaterials.

The anode current collector is typically fabricated to a thickness of 3to 500 μm. The anode current collector is not particularly limited solong as it does not cause chemical changes in the fabricated battery andhas conductivity. For example, the anode current collector may be madeof copper, stainless steel, aluminum, nickel, titanium, sintered carbon,copper or stainless steel surface-treated with carbon, nickel, titanium,or silver, and aluminum-cadmium alloys. Similar to the cathode currentcollector, the anode current collector may also have fine irregularitiesat a surface thereof to enhance adhesion between the anode currentcollector and the anode active material and may be used in various formsincluding films, sheets, foils, nets, porous structures, foams, andnon-woven fabrics.

The separator is disposed between the cathode and the anode and, as theseparator, a thin insulating film with high ion permeability and highmechanical strength is used. The separator generally has a pore diameterof 0.01 to 10 μm and a thickness of 5 to 300 μm. As the separator, forexample, sheets or non-woven fabrics, made of an olefin-based polymersuch as polypropylene; or glass fibers or polyethylene, which havechemical resistance and hydrophobicity, are used. When a solidelectrolyte such as a polymer or the like is used as an electrolyte, thesolid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte consists of anon-aqueous electrolyte and lithium. As the non-aqueous electrolyte, anon-aqueous electrolyte solution, a solid electrolyte or the like may beused.

Examples of the non-aqueous electrolyte solution include non-aproticorganic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate,ethylene carbonate, butylene carbonate, dimethyl carbonate, diethylcarbonate, gamma-butyrolactone, 1,2-dimethoxy ethane, tetrahydrofuran,2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide,dimethylformamide, dioxolane, acetonitrile, nitromethane, methylformate, methyl acetate, phosphoric acid triester, trimethoxy methane,dioxolane derivatives, sulfolane, methyl sulfolane,1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives,tetrahydrofuran derivatives, ether, methyl propionate, and ethylpropionate.

Examples of the organic solid electrolyte include polyethylenederivatives, polyethylene oxide derivatives, polypropylene oxidederivatives, phosphoric acid ester polymers, polyagitation lysine,polyester sulfide, polyvinyl alcohols, polyvinylidene fluoride, andpolymers containing ionic dissociation groups.

Examples of the inorganic solid electrolyte include, but are not limitedto, nitrides, halides and sulfates of lithium (Li) such as Li₃N, LiI,Li₅NI₂, Li₃N—LiI—LiOH, LiSiO₄, LiSiO₄—LiI—LiOH, Li₂SiS₃, Li₄SiO₄,Li₄SiO₄—LiI—LiOH, and Li₃PO₄—Li₂S—SiS₂.

The lithium salt is a material that is readily soluble in thenon-aqueous electrolyte and examples thereof include, but are notlimited to, LiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃,LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li, (CF₃SO₂)₂NLi,chloroborane lithium, lower aliphatic carboxylic acid lithium, lithiumtetraphenyl borate, and imides.

In addition, in order to improve charge/discharge characteristics andflame retardancy, for example, pyridine, triethylphosphite,triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphorictriamide, nitrobenzene derivatives, sulfur, quinone imine dyes,N-substituted oxazolidinone, N,N-substituted imidazolidine, ethyleneglycol dialkyl ether, ammonium salts, pyrrole, 2-methoxy ethanol,aluminum trichloride or the like may be added to the non-aqueouselectrolyte. If necessary, in order to impart incombustibility, theelectrolyte may further include halogen-containing solvents such ascarbon tetrachloride and ethylene trifluoride. Further, in order toimprove high-temperature storage characteristics, the non-aqueouselectrolyte may further include carbon dioxide gas.

In addition, the present invention also provides a battery moduleincluding the lithium secondary battery as a unit battery and a batterypack including the battery module.

The battery pack may be used as a power source of devices that requirehigh-voltage stability, long cycle characteristics, high ratecharacteristics, and the like.

Preferable examples of the devices include, but are not limited to,electric motor-driven power tools; electric vehicles (EVs), hybridelectric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs);electric two-wheeled vehicles such as e-bikes and e-scooters; electricgolf carts; and systems for storing power.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanying drawing,in which:

FIG. 1 is a scanning electron microscopy (SEM) image of a precursorprepared according to Example 1, which was captured using FE-SEM (modelS-4800 available from Hitachi);

FIG. 2 is a scanning electron microscopy (SEM) image of a precursorprepared according to Example 2, which was captured using FE-SEM (modelS-4800 available from Hitachi);

FIG. 3 is a scanning electron microscopy (SEM) image of a precursorprepared according to Comparative Example 1, which was captured usingFE-SEM (model S-4800 available from Hitachi); and

FIG. 4 is a scanning electron microscopy (SEM) image of a precursorprepared according to Comparative Example 2, which was captured usingFE-SEM (model S-4800 available from Hitachi).

BEST MODE

Now, the present invention will be described in more detail withreference to the following examples. These examples are provided forillustration of the present invention only and should not be construedas limiting the scope and spirit of the present invention.

Example 1

After filling a 4 L wet reactor tank with 3 L of distilled water,nitrogen gas was continuously added to the tank at a rate of 2 L/min toremove dissolved oxygen. Here, the temperature of distilled water in thetank was maintained at 50□ using a temperature maintenance device. Inaddition, the distilled water in the tank was stirred at 1000 to 1500rpm using an impeller connected to a motor installed outside the tank.

Manganese sulfate, nickel sulfate, and cobalt sulfate were mixed in amolar ratio of 0.50:0.45:0.05 to prepare a 1.5 M aqueous transitionmetal solution. Subsequently, to substitute anion sites, 0.5 mol % ofphosphate and 4.0 mol % of sucrose which provide PO₄ anions were mixedtherewith. Separately, a 3 M aqueous sodium hydroxide solution wasprepared. The aqueous transition metal solution was continuously pumpedinto the wet reactor tank, using a metering pump, at a rate of 0.18L/hr. The aqueous sodium hydroxide solution was pumped in arate-variable manner by a control unit for adjusting a pH of thedistilled water in the tank such that the distilled water in the wetreactor tank was maintained at a pH of 11.5. In this regard, a 14%ammonia solution as an additive was continuously co-pumped to thereactor at a rate of 0.04 L/hr.

Flow rates of the aqueous transition metal solution, the aqueous sodiumhydroxide solution and the aqueous ammonia solution were adjusted suchthat an average residence time of the solutions in the wet reactor tankwas approximately 6 hours. After the reaction in the tank reached asteady state, a certain duration of time was given to synthesize acomposite transition metal precursor with a higher density.

After reaching the steady state, the manganese-nickel compositetransition metal precursor, which was prepared by 20-hour continuousreaction of transition metal ions of the aqueous transition metalsolution, hydroxide ions of the sodium hydroxide and ammonia ions of theammonia solution, was continuously obtained through an overflow pipeinstalled on the top side of the tank.

The resulting composite transition metal precursor was washed severaltimes with distilled water and dried in a 120° C. constant-temperaturedrying oven for 24 hours to obtain a manganese-nickel compositetransition metal precursor.

Example 2

A transition metal precursor was prepared in the same manner as inExample 1, except that sucrose was not mixed with the aqueous transitionmetal solution.

Comparative Example 1

A transition metal precursor was prepared in the same manner as inExample 1, except that phosphate was not mixed with the aqueoustransition metal solution.

Comparative Example 2

A transition metal precursor was prepared in the same manner as inExample 1, except that sucrose and phosphate were not mixed with theaqueous transition metal solution.

Experimental Example 1

SEM images of the transition metal precursors prepared according toExamples 1 and 2, and Comparative Examples 1 and 2, respectively,captured using FE-SEM (model S-4800 available from Hitachi), areillustrated in FIGS. 1 to 4.

Referring to FIGS. 1 to 4, it can be confirmed that the transition metalprecursor of Example 1 using 2 mol % of sucrose exhibited strongercohesive strength of primary particles than that of the precursor ofComparative Example 1 and thus particles of the precursor of Example 1had a more spherical shape

Referring to FIG. 1 to FIG. 4, it was confirmed that the precursorprepared according to Example 1, which uses sucrose and anion sites ofwhich were substituted with PO₄, has many pores, a wide specific surfacearea and a uniform diameter, when compared with the precursors preparedaccording to Comparative Examples 1 and 2. In addition, it was confirmedthat, in the precursor prepared according to Example 1, primaryparticles exhibited improved cohesive force and thereby particlecrystallizability and particle spheroidization degree were improved.Furthermore, it was confirmed that, although sucrose was not used, theprecursor prepared according to Example 2, anion sites of which weresubstituted with PO₄, exhibited improved particle crystallizability andparticle spheroidization degree, when compared with the precursorsprepared according to Comparative Examples 1 and 2.

Experimental Example 2

The tap densities of the precursors prepared according to Examples 1 and2, and Comparative Examples 1 and 2, respectively, were measured andsummarized in Table 1 below.

TABLE 1 Tap density (g/cc) Example 1 1.54 Example 2 0.95 Comparative0.55 Example 1 Comparative 0.80 Example 2

As shown in Table 1, it can be confirmed that the precursors preparedaccording to Examples 1 and 2, anion sites of which were substituted,exhibit improved tap densities, when compared with the precursorsprepared according to Comparative Examples 1 and 2, anion sites of whichwere not substituted. Such a result is caused by easy precipitation ofthe transition metal hydroxide due to anion sites substituted with PO₄and thereby improved crystallizability and cohesive force of the primaryparticles.

Examples 3 and 4, and Comparative Examples 3 and 4

Manufacture of Coin Cell

Each of the manganese-nickel-cobalt composite transition metalprecursors prepared according to Examples 1 and 2, and ComparativeExamples 1 and 2 was mixed with Li₂CO₃ in accordance with the molarratio of each composition and then sintered at 900 to 950° C. for 5 to10 hours by heating at a heating rate of 3 to 5° C./min to prepare acathode active material powder.

The prepared cathode active material powder, Denka as a conductivematerial, and KF1100 as a binder were mixed in a weight ratio of95:2.5:2.5 to prepare a slurry. The slurry was uniformly coated on Alfoil having a thickness of 20 μm. The coated Al foil was dried at 130°C., thereby completing fabrication of a cathode for a lithium secondarybattery.

The fabricated cathode for a lithium secondary battery, lithium metalfoil as a counter electrode (i.e., an anode), a polyethylene membrane asa separator (Celgard, thickness: 20 μm), and a liquid electrolytecontaining 1 M LiPF₆ dissolved in a mixed solvent of ethylene carbonate,dimethylene carbonate, and diethyl carbonate in a volume ratio of 1:2:1were used to manufacture a 2016 coin cell.

Experimental Example 3

Initial Charge and Discharge Characteristics

Electrical characteristics of the cathode active material of each ofcoin cells manufactured according to Examples 3 and 4, and ComparativeExamples 3 and 4 were evaluated at 3.0 to 4.4 V using an electrochemicalanalyzer (Toscat 3100U available from Toyo Systems).

To evaluate performance of each coin cell, charge and discharge capacityof each coin cell was measured at a current of 1 C and at a voltagerange of 3.0 to 4.4 V. Results of discharge capacities and charge anddischarge efficiencies of the coin cells are summarized in Table 2below.

TABLE 2 Initial charge Initial discharge Initial charge and capacitycapacity discharge efficiency Samples (mAh/g) (mAh/g) (%) Example 3 185172 93 Example 4 183 169 92 Comparative 169 153 90 Example 3 Comparative180 162 90 Example 4

As shown in Table 2, it can be confirmed that the precursors preparedaccording to Examples 1 and 2, anion sites of which were substituted,have superior initial charge and discharge capacity and efficiency, whencompared with the precursors prepared according to Comparative Examples1 and 2, anion sites of which were not substituted.

Experimental Example 4

Lifespan Characteristics

Each of coin cells manufactured according to Examples 3 and 4, andComparative Examples 3 and 4 was charged and discharged thirty times ata current of 0.5 C to evaluate lifespan characteristics. Results aresummarized in Table 3 below.

TABLE 3 Lifespan characteristics 30^(th)/1^(st) discharge capacity (%)Example 3 97.0 Example 4 92.0 Comparative 92.2 Example 3 Comparative96.0 Example 4

As shown in Table 3, it can be confirmed that the precursor preparedaccording to Example 1, which uses sucrose and anion sites of which weresubstituted with PO₄, exhibits lifespan characteristics of 97%, which isthe highest value.

Experimental Example 5

Output Characteristics

To evaluate output characteristics, each of coin cells manufacturedaccording to Examples 3 and 4, and Comparative Examples 3 and 4 wascharged and discharged at a current of 0.5 C and then discharged at acurrent of 1.0 C and 2.0 C. Results are summarized in Table 4 below.

TABLE 4 0.1 C discharge 2 C discharge Output capacity capacitycharacteristics (mAh/g) (mAh/g) 0.1 C/2.0 C (%) Example 3 172 146 85Example 4 172 136 79 Comparative 155 121 78 Example 3 Comparative 166112 67 Example 4

As shown in Table 4, it can be confirmed that the precursors preparedaccording to Examples 1 and 2, anion sites of which were substituted,exhibit improved output characteristics when compared with theprecursors prepared according to Comparative Examples 1 and 2, anionsites of which were not substituted.

Those skilled in the art will appreciate that various modifications,additions and substitutions are possible, without departing from thescope and spirit of the invention as disclosed in the accompanyingclaims.

INDUSTRIAL APPLICABILITY

As described above, a transition metal precursor for preparing a lithiumcomposite transition metal oxide according to the present invention isprepared in a state including a reducing agent to prevent oxidation ofMn and, as such, a precursor having a larger specific surface area and auniform diameter may be synthesized. At the same time, by substitutinganion sites, precipitation suppression due to addition of a reducingagent may be solved and, as such, the crystallizability, spheroidizationdegree and tap density of the precursor may be improved.

In addition, when a lithium composite transition metal oxide preparedusing the precursor is used as a cathode active material, an electrodeprocess becomes easy and a secondary battery based on the lithiumcomposite transition metal oxide may exhibit excellent initial dischargecapacity and efficiency, and improved output characteristics andlifespan characteristics.

The invention claimed is:
 1. A method of preparing a transition metalprecursor comprising: preparing an aqueous transition metal solutioncomprising a transition metal-containing salt for preparing a precursorhaving a first anion; mixing a second anion selected from the groupconsisting of PO₄, BO₃, CO₃, F and NO₃ and a reducing agent with theaqueous transition metal solution to substitute anion sites of theprecursor; and co-precipitating by adding a strong base after the mixingto form the transition metal precursor having a composition representedby Formula 1 below:Mn_(a)M_(b)(OH_(1-x))_(2-y)A_(y)  (1) wherein M is Ni and Co; A is atleast one selected from the group consisting of anions of PO₄, BO₃, CO₃,F and NO₃; 0.5≤a≤1.0; 0≤b≤0.5; a+b=1; 0<x<1.0; and 0<y≤0.02; wherein thereducing agent is a sugar-based material; and wherein the transitionmetal-containing salt consists of a transition metal cation and thefirst anion.
 2. The method according to claim 1, wherein the reducingagent has a concentration of 2.0 to 7.0 mol % based on a molar amount ofthe aqueous transition metal solution.